Drilling and cementing with blast furnace slag/silicate fluid

ABSTRACT

A drilling and cementing operation is carried out utilizing a universal fluid comprising blast furnace slag, water, a silicate and a retarder, the components of the drilling fluid being chosen so as to have a dual functionality in promoting the drilling fluid and thereafter in being functional constituents of a cementitious slurry.

BACKGROUND OF THE INVENTION

This invention relates to drilling and cementing boreholes.

The drilling of boreholes is generally carried out using a rotarydrilling process. The rotary drilling of a borehole is accomplished byrotating a drill string having a drill pipe and a drill bit at its lowerend. Weight is applied to the drill bit while rotating to create aborehole into the earth. The drill string is hollow and sections areadded to the drill string to increase its length as the borehole isdeepened. This rotary drilling process creates significant amounts offriction which produces heat along with fragments of the strata beingpenetrated. The fragments of the strata must be removed from theborehole and the drill bit must be cooled to extend its useful life.Both of these necessities are accomplished by the circulation of a fluiddown through the drill string and up to the surface between the drillstring and the wall of the borehole.

Once the borehole has been drilled to the desired depth, it may bedesirable to isolate the separate areas, zones or formations transversedby the borehole. For extraction of fluids from formations, a conduit(casing) must be inserted into the borehole extending from the surfacedownward, and liners may be hung inside the casing.

At this point it becomes necessary to fill the annulus between thecasing and the borehole wall or between the liner and casing with amaterial which will seal the annulus (interfacial sealing) to inhibitcommunication between various formations penetrated by the wellbore andwhich will provide structural support for the casing or liner. This iscommonly referred to as primary cementing.

Bonding of the cement to the casing and borehole surfaces is critical toproviding an effective seal in the annulus and for providing support forcasings. Under most conditions, the bonding of cement to casing isachieved through contact of the cement particles with the surface of thecasing. The resulting region of contact provides a mechanical interfacewhich impedes movement of the casing due to high frictional forces. Afluid seal between cement and casing is also effected by the closecontact of the cement particles at the casing surfaces which results ina region of very low effective permeability that prevents fluidmigration along the interface.

Bonding between the cement and borehole wall is also achieved throughcontact of the cement particles with the formation of drilling fluidfilter cake commonly deposited at the borehole wall during the drillingof the borehole. However, bonding or interfacial sealing between thecement and borehole surfaces is not readily achievable. Cowan and Hale,U.S. Pat. No. 5,020,598 (Jun. 4, 1991) broadly disclose improved cementto casing sealing through the addition of a polyalcohol.

Generally, the borehole into which the casing or liner is introduced isfilled with drilling mud. Conventional Portland cement and conventionaldrilling muds are incompatible. Thus, a mixture of conventional Portlandcement and conventional drilling mud will not set up into a strongcement. In addition, the viscosity of such mixtures becomesuncontrollable and may either become too viscous to pump or may getthinner.

At the completion of drilling, the used drilling fluid is displaced fromthe borehole using some means to keep it separate from the cement tofollow. This creates two problems. First, the means developed by theindustry to keep the drilling fluid separate is relatively complex,involving the use of a landing collar and a pair of wiper plugs. Inaddition, the thus-displaced drilling fluid must be disposed of. Wyantet al, U.S. Pat. No. 3,499,491 (Mar. 10, 1970) proposed a partialsolution to this problem by mixing a cementitious material such asPortland cement with powdered sodium silicate glass and a treateddrilling fluid. While this does solve the problem of drilling fluiddisposal since the drilling fluid is incorporated into the cement, itnecessitates the use of extraneous components in order to achieve asufficient degree of compatibility to make the cement work at all.

It would be desirable to have a drilling fluid where most or all of thecomponents have both a drilling fluid function and a cementitiousfunction. It would also be desirable to have a cementitious slurry madefrom a drilling fluid wherein all of the ingredients are compatible.Even where cements can be made by adding cementitious materials todrilling fluids, ingredients in the drilling fluid adversely affect thefinal cement even when they can be rendered sufficiently compatible tobe operable. Peterson U.S. Pat. No. 4,780,220 (Oct. 25, 1988) disclosesa conventional drilling fluids containing a polyglycerine component.Clarke, U.S. Pat. No. 4,897,119 (Jan. 30, 1990) discloses alkali metalsilicates as accelerators in blast furnace slag grouts. Tragesser, U.S.Pat. No. 3,557,876 (Apr. 10, 1969) discloses various pozzolans indrilling fluids and, along with matreials such as calcium oxide, incementitious materials.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a universal drilling fluidwhich is transformable to a cement.

It is a further object of this invention to provide a drilling fluidhaving components characterized by dual functionality in promoting boththe drilling operation and the cementing operation.

It is yet a further object of this invention to provide a universalfluid transformable into a cement without the addition of extraneouscompatibility additives.

It is yet a further object of this invention to improve interfacialsealing.

In accordance with this invention, drilling is carried out utilizing afluid comprising water, blast furnace slag, a silicate and a retarder.Thereafter the drilling fluid is activated to produce a cement.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that a drilling fluid transformable to a cement can beproduced utilizing components which are characterized by (a) dualfunctionality in promoting both the drilling operation and the cementingoperation and, (b) compatibility with each other. Such a universal fluidavoids the problems of incompatibility and the necessity for addingextraneous compatibilizing agents and further avoids a compromise on thequality of the drilling fluid and the cement.

Definitions

In this description, the term "universal fluid" means a blast furnaceslag-containing aqueous composition suitable for drilling which, onactivation, sets up into a cement.

By "cementitious slurry" is meant a slurry comprising blast furnace slagand ingredients which cause the slurry to harden.

By "direct fluid contact" between the displacement fluid and thecementitious slurry is meant that the displacement fluid directlycontacts the upper surface of the column of cementitious slurry asopposed to having a solid wiper plug and/or spacer fluid disposedbetween the cementitious slurry and the displacement fluid. By "directfluid contact" between the cementitious slurry and the drilling fluid ormud is meant that the cementitious slurry directly contacts the uppersurface of the column of drilling fluid or mud as opposed to having awiper plug with a rupturable diaphragm and/or spacer fluid disposedbetween the cementitious slurry and the drilling fluid or mud.

The term "pipe" means either a casing or a liner.

The term "primary cementing" refers to any cementing operation wherein acementitious slurry is passed into an annulus surrounding a pipe andthus encompasses both the cementing of casings wherein the annulus isbetween the casing and the borehole wall and the cementing of linerswhere the annulus includes an annulus between the liner and the casing.

By "activator system" is meant either a single activator or a mixture ofactivators.

By "cuttings" stabilizer is meant a material which inhibitsdisintegration of cuttings which is indicative of a wellbore or shale orformation stabilizer.

By "borehole stabilizer" or "wellbore stabilizer" is meant an additiveor system of additives that reduces the stress state of the wellboreand/or modifies the wellbore such that strength of the formation isenhanced or chemically passivates clays in formation pores to reduceformation damage (reduced effective permeability).

By "shale stabilizer" is meant an additive or additive system whichstabilizes cuttings which is indicative of the ability to stabilize aborehole (wellbore).

By "soluble", as it relates to polyalcohols, is meant a materialcontaining alcohol and generally ether linkages which, primarily becauseof a low ratio of ether to alcohol linkages, is sufficiently soluble inwater at room temperature that at least 80 grams will dissolve in 100grams of water. Lower molecular weight also tends to make thepolyalcohols more soluble.

By "insoluble", as it relates to alcohols, is meant a materialcontaining alcohol and generally ether linkages which, primarily becauseof a high ratio of ether to alcohol linkages, or hydrocarbon chains fromdihydric monomers, is substantially insoluble in water at roomtemperature. Higher molecular weight also tends to make the alcoholsmore insoluble. Generally, the incoluble alcohol is a polyol, too.

As used herein "down" or "in" as it relates to a drill string or casingmeans in a direction toward the farthest reach of the borehole eventhough in some instances the borehole can be disposed in a horizontalposition. Similarly, "up" or "out" means back toward the beginning ofthe borehole.

Universal Fluid Composition

The universal fluid comprises:

a) an aqueous medium,

b) blast furnace slag,

c) a silicate

d) a retarder

e) generally a secondary fluid loss additive,

f) generally a secondary rheology control agent (viscosifier),

g) optionally, a weight material (as needed),

h) optionally, a shale stabilizer (as needed),

i) optionally, a deflocculant (as needed).

The above description does not, however, dictate that the compositionwill have at least nine ingredients just for the drilling function.Another novel feature of this invention is the use of components which(a) have a dual functionality in that they have an important drillingfluid function and an important cementitious slurry function, and (b)may have two or more drilling fluid functions and/or two or morecementitious slurry functions. The silicate, for instance, functions asa viscosifier and a shale stabilizer in the drilling fluid and thencontinues to function as a shale stabilizer in the subsequentcementitious slurry as well as acting as accelerator as is discussed inmore detail hereinbelow.

Aqueous Medium

The term "aqueous medium" is intended to encompass both fresh water andsalt water, including any fluid having water as the continuous phase,including oil-in-water emulsions, as well as essentially oil-free waterbased drilling fluids.

It is generally desired that the drilling fluids use water containingdissolved salts, particularly sodium chloride. In these instances, 0.1to 26 wt %, preferably 3 to 20 wt % sodium chloride based on the weightof the continuous phase may be used. One suitable source is to useseawater or a brine solution simulating seawater. The strength of theresulting cement is actually enhanced by the salt which is contrary towhat would be expected in view of the intolerance of Portland cement tobrine. Various salts, including organic salts, are suitable for use inthe drilling fluid used in this invention in addition to, or instead ofNaCl, including, but not limited to, NaBr, KCl, CaCl₂, NANaNO₃, NaC₂ H₃O₂, KC₂ H₃ O₂, NaCHO₂, CsCHO₂ and KCHO₂. Sodium chloride is usuallypreferred, as noted above. These salts can be used, if desired, from 0.1wt % up to the saturation point under the conditions employed.

The use of a salt solution such as seawater is particularly advantageousbecause salts such as sodium chloride act as a shale stabilizer in thedrilling fluid in addition to enhancing the strength of the cement asnoted hereinabove.

The salt modification of the aqueous phase to lower the water activityand increase the ionic strength results in stabilized cuttings as wellas actual wellbore stabilization.

Blast Furnace Slag

Blast furnace slag is an essential ingredient of the universal fluidcomposition used in this invention. It serves as a latent cementitiouscomponent in the drilling fluid and further serves in the cementitiousslurry as the cementitious constituent.

While setting must be retarded during drilling, the blast furnace slagis still a desired and essential ingredient in the drilling fluid fortwo reasons. First, it allows laying down a settable filter cake duringdrilling. Second, it provides a compatible residual material in theborehole for the cementitious slurry.

By "blast furnace slag" is meant the hydraulic refuse from the meltingof metals or reduction of ores in a furnace. Such material is disclosedin Hale and Cowan, U.S. Pat. No. 5,058,679 (Oct. 22, 1991), thedisclosure of which is incorporated herein by reference.

The preferred blast furnace slag used in this invention is a high glasscontent slag produced by quickly quenching a molten stream of slag at atemperature of between 1400° C. and 1600° C. through intimate contactwith large volumes of water. Quenching converts the stream into amaterial in a glassy state having hydraulic properties. At this stage itis generally a granular material that can be easily ground to thedesired degree of fineness. Silicon dioxides, aluminum oxides, ironoxides, calcium oxide, magnesium oxide, sodium oxide, potassium oxide,and sulphur are some of the chemical components in slags. Preferably,the blast furnace slag used in this invention has a particle size suchthat it exhibits a Blaine specific surface area between 2,000 cm² /g and15,000 cm² /g and more preferably, between 3,000 cm² /g and 15,000 cm²/g, even more preferably, between 4,000 cm² /g and 9,000 cm² /g, mostpreferably between 4,000 cm² /g and 8,500 cm² /g. An available blastfurnace slag which fulfills these requirements is marketed under thetrade name "NEWCEM" by the Blue Circle Cement Company. This slag isobtained from the Bethlehem Steel Corporation blast furnace at SparrowsPoint, Md.

A usual blast furnace slag composition range in weight percent is: SiO₂,30-40; Al₂ O₃, 8-18; CaO, 35-50; MgO, 0-15; iron oxides, 0-1; S, 0-2 andmanganese oxides, 0-2. A typical specific example is: SiO₂, 36.4; Al₂O₃, 16.0; CaO, 43.3; MgO, 3.5; iron oxides, 0.3; S, 0.5; and manganeseoxides, <0.1.

Blast furnace slag having relatively small particle size is frequentlydesirable when used to form the cementitious slurry because of thegreater strength it imparts in many instances to a final cement.

Characterized in terms of particle size the term "fine" can be used todescribe particles with a Blaine specific surface area in the range of4,000 to 7,000 cm² /g, corresponding to 16 to 31 microns in size;"microfine" can be used to describe those particles with a Blainespecific surface area from greater than 7,000 cm² /g to 10,000 cm² /gthat correspond to particles of 5.5-16 microns in size and "ultrafine"can be used to describe particles with a Blaine specific surface areaover 10,000 cm² /g that correspond to particles 5.5 microns and smallerin size. Small particle size blast furnace slags are available from BlueCircle Cement Company, Koch Minerals, Wichita, Kans., under the tradename "WELL-CEM", and from Geochem under the trade name "MICROFINEMC100".

However, it is very time consuming to grind blast furnace slag to theseparticle sizes. It is not possible to grind blast furnace slag in amanner where particles are entirely one size. Thus, any grindingoperation will give a polydispersed particle size distribution. A plotof particle size versus percent of particles having that size would thusgive a curve showing the particle size distribution.

A blast furnace slag having a polydispersed particle size distributionexhibiting at least two nodes on a plot of particle size versus percentof particles in that size can be utilized. It has been found that ifonly a portion of the particles are in the ultrafine category, theremaining, indeed the majority, of the slag can be ground more coarselyand still give essentially the same result as is obtained from the moreexpensive grinding of all of the blast furnace slag to an ultrafinestate. Thus, a grinding process which will give at least 5% of itsparticles falling within a size range of 1.9 to 5.5 microns offers aparticular advantage in economy and effectiveness. More preferably, 6 to25 wt % would fall within the 1.9 to 5.5 micron range. The moststraightforward way of obtaining such a composition is simply to grind aminor portion of the blast furnace slag to an ultrafine condition andmix the resulting powder with slag ground under less severe conditions.Even with the less severe conditions there would be some particleswithin the fine, microfine or ultrafine range. Thus, only a minority,i.e., as little as 4 wt % of the slag, would need to be ground to theultrafine particle size. Generally, 5 to 25 wt %, more preferably 5 to10 wt %, can be ground to the ultrafine particle size and the remainderground in a normal way thus giving particles generally in a size rangeof greater than 11 microns, the majority being in the 11 to 31 micronrange.

In some instances, it may be desirable in the final cementitious slurryto use a mixture of the blast furnace slag and Portland cement. If suchadditional component is incorporated into the drilling fluid to producethe cementitious slurry, it can be incorporated in an amount within therange of 1 to 100 wt % of the weight of the blast furnace slag in thecementitious slurry, preferably 10 to 99 wt %, more preferably 15 to 50wt %. That is, at 100 wt %, the weight ratio would 1:1. The basis hereis the total blast furnace slag actually in the cementitious slurry,including that carried over from the drilling operation and any addedalong with the activator. The Portland cement acts as an activator forthe blast furnace slag and thus in one embodiment, no other activator isutilized.

Silicate

The silicates broadly encompass any silicate salt, or silicic acid whichwill form a salt in the drilling fluid. Alkali metal soluble silicatessuch as sodium silicate are preferred. Applicable silicates asexemplified by sodium silicate are those having a SiO₂ :Na₂ O weightratio within the range of 1.6 to 3.5.

Retarder

Retarders are generally used in an amount within the range of 0.1 to 30,preferably 5 to 25 volume percent based on volume of drilling fluid or0.1 to 30, preferably 5 to 25 wt % based on the weight of the continuous(fluid) phase of the drilling fluid.

A retarder is an essential ingredient of the universal fluid compositionused in this invention. Organic compounds in general and morespecifically, low molecular weight organic acids, are suitableretarders. Lignosulfonates, including both chrome lignosulfonate andchrome-free lignosulfonate, can serve as retarders.

Retarders are generally compounds which have OH⁻, COOH, BO₃ or BO⁻ ₄functional groups which are a part of or can be released from thecompound in solution. Chelating agents are also retarding agents. Suchagents include lignosulfates, citric acid, EDTA, and borax. Otherretarding materials include phosphonates, such as those used in scaleinhibition in oil and gas wells and also in water treatment processesfor boilers, cooling towers, etc. Examples of such materials are thosemarketed by Monsanto Company under the trade name "DEQUEST". Specificexamples are DEQUEST 2000, 2006, 2010, 2016, 2060, and 2066.

Other retarding materials include some phosphates such as sodium,potassium, calcium or magnesium glycerophosphates, borates such as boricacid and its salts, salts of organic acids such as sodium or potassiumgluconate, sodium or potassium glucoheponate and sodium citrate. Organicamines can also be retarders.

Combinations of borax, boric acid or other borate salts and some borateester surfactants such as monoethanolamine borate with lignosulfonate ororganic acid salts are good high temperature retarders. These arecommonly used for high temperature retarders for cements. Salts oforganic polyacids such as EDTA, polyacrylic acid, polymethacrylic acid,itaconic acid, fumaric acid can also retard in some temperature ranges.

Polyalcohols represent another class of very effective retarders.Discussed in detail hereinbelow are suitable cyclic polyols, ethoxylatedpropoxylated alcohols and epoxy-containing cyclic polyetherpolyols.

Polyalcohols Broadly

Suitable polyalcohols include polyols having at least two carbon atomsand two hydroxyl groups but no more than 18 carbon atoms and 13 hydroxylgroups. Nonlimitative examples of such polyalcohols include (carbonchains may be straight chains, branched chains or cyclic, ethyleneglycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol (propyleneglycol), neopentyl glycol, pentaerythritol, 1,6-hexanediol, glycerol,open and cyclic condensation products of glycerol (and/or otherpolyalcohols) such as diglycerols, triglycerols, tetraglycerols,pentaglycerols, and hexaglycerols, poly(ethylene glycol)s,poly(propylene glycol)s, ethylenepropylene glycol, polyethylenepropyleneglycols, ethylenepropylene glycol copolymers and ethylenebutylene glycolcopolymers and ethylenebutylene glycol copolymers, 1,5,6,9-decanetetrol,1,1,4,4-cyclohexanetetramethanol, 1,2,4,5-cyclohexanetetramethanol,1,4-cyclohexanedimethanol, 1,3-cyclopentanedimethanol,1,2,4,7-heptanetetrol, 1,2,3,5-heptanetetrol, 1,5,8-nonanetriol,1,5,9-nonanetriol, 1,3,5,9-nonanetetrol, 1,3,5-heptanetriol,2,4,6-heptanetriol, 4,4-dimethyl-1,2,3-pentanetriol,1,1,3-cyclohexanetrimethanol, 1,3,4-cycloheptanetriol,1,1-cyclopropanediol, 1,2-cyclopropanediol, 1,2,3-cyclopropanetriol,1,1-cyclopropanedimethanol, 1,2-cyclopropanedimethanol,1,2,3-cyclopropanetrimethanol, 1,1-cyclobutanediol, 1,2-cyclobutanediol,1,3-cyclobutanediol, 1,2-cyclobutanedimethanol, 1,2,3-cyclobutanetriol,1,2,4-cyclobutanetriol, 1,2,3,4-cyclobutanetetrol,1,3-dimethyl-1,2,3,4-cyclobutanetetrol, 1 hydroxy cyclobutanemethanol,2-methyl-1,2-butanediol, 2-methyl-1,2-butanediol,3-methyl-2,2-butanediol, 1,2-pentanediol, 1,3-pentadiol,1,4-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,2,3-pentanetriol,1,2,4-pentanetriol, 2,3,4-pentanetriol, 1,1-cyclopentanediol,1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2,3-cyclopentanetriol,1,2-hexanediol, 1,3-hexanediol, 1,2,3-hexanetriol, 1,2,4-hexanetriol,1,2,3,4-hexanetetrol, 1,1-cyclohexanediol, 1,2-cyclohexanediol,1,4-cyclohexanediol, 1,2,4-cyclohexanetriol, 1,2,5-cyclohexanetriol,1,2,3,4-cyclohexanetetrol, and 1,2,3,5-cyclohexanetetrol and mixturesthereof.

Cyclic Polyol Production

A general chemical composition formula, disregarding the order,representative of one class of polyols is as follows: ##STR1## where x≧1and y≧0.

As a specific example, x=2 and y=5. Also of significance is theether-to-alcohol ratio which is given by the following formula (forpolyetherpolyols produced from glycerol): ##EQU1## where e=the ratio,x=the number of rings and y=the number of glycerol moleculesincorporated into the molecule that are not in the rings. If x=0 thenthe ratio varies from 0.25 to a value approaching 1. Preferably x is not0, i.e., preferably the polyol is a polyethercyclicpolyol. The typical erange for such polyalcohols is 1.4 to 1.8. The sum of 2x+y yields thenumber of glycerol monomers constituting the polymer.

A more complete description of these polyether-cyclicpolyols is found inHale and Cowan, U.S. Pat. No. 5,058,679 (Oct. 22, 1991), the disclosureof which is incorporated herein by reference.

Broadly, the reaction involves heating a polyol with at least threehydroxyl groups, at least two of which are adjacent each other, withremoval of water to form a condensed product.

With glycerol as the primary reaction medium, it is preferable to removeat least 1.05 and more preferably, at least approximately 1.12 but nomore than 1.2 moles of water per mole of glycerol. Most preferably, 1.12to 1.15 moles of water per mole of glycerol in the product should beremoved. If the feed contains an appreciable amount of predehydratedglycerol polymers, then the remaining dehydration will be less than 1.2moles per mole of glycerol. As an example, for a known commercialproduct which typically contains 15 percent by weight ofbis(hydroxymethyl)-dioxanes, and 85 percent by weight of glycerol, thedehydration can be calculated as follows. For approximately 100 grams offeed there are 85 grams of glycerol (0.92 moles) and 15 grams ofbis(hydroxymethyl)-dioxane (0.1014 moles). The glycerol component willhave to lose 0.92×1.2=1.104 moles of water. The 0.1014 moles ofbis(hydroxymethyl)-dioxane is derived from 0.2028 moles of glycerol byremoval of 0.2028 moles of water; 1.2 total moles water per mole ofglycerol should be removed, i.e., 0.2028×1.2=0.2434 moles. Thus, it isnecessary to remove 0.2434-0.2028=0.0406 moles of water. The total to beremoved is 1.104 moles from the glycerol+0.0406 moles from thebis(hydroxymethyl)-dioxane=1.1496 moles water (or approximately 1.15moles) from the 100 grams of the known commercial product.

Therefore, it is necessary to remove close to 1.2 moles of water foreach mole of glycerol which enters into the condensation of an initiallypartially dehydrated glycerol feed stream. Alternatively, in most casesinvolving complex feed streams, it would be appropriate to carry out thereaction and select a final maximum reaction temperature at set pressureconditions, such as is known from previous experience to yieldsatisfactory polyethercyclicpolyol preparations.

From 5 to 35 wt % of the polyol can be replaced with a dihydroxy alcoholif it is desired to make a less water-soluble product. Suitabledihydroxy alcohols include those having 2 to 18 carbon atoms, preferablythose having 4 to 14 carbon atoms. Suitable dihydroxy alcohols includeethylene glycol, propylene glycol, diethylene glycol and triethyleneglycol, for instance.

The solubility in water is a function of molecular weight, the presenceor absence of long chain dihydric alcohol units, and ether units, witheither higher molecular weight, long chain dihydric alcohols or higherether ratios, or all three, giving insoluble polyols.

Epoxy-containing Polyethercyclicpolyols

In some instances it may be desirable to use a polyol containingparaffinic and/or aromatic groups linked by ether linkages to the polyolstructure, those linkages having their origin in glycidyl ether or epoxygroups. Such polyols can be produced as disclosed in said Hale and Cowanpatent for polyethercyclicpolyols generally except an epoxy resin isincorporated by reaction. Specifically, they can be produced by:

(a) heating a reaction mixture comprising a reactant selected from thegroup consisting of (1) a polyol having at least three hydroxyl groupsof which at least two of the hydroxyl groups are vicinal, (2) precursorsof the polyol, (3) cyclic derivatives of the polyol, and (4) mixturesthereof, said heating initiating the thermal condensation:

(b) removing water formed during the thermal condensation as describedabove in connection with cyclic polyol production; and

(c) prior to the condensation going to completion, admixing an epoxyresin with the reaction mixture.

Epoxy resins are characterized by the presence of a three-memberedcyclic ether group commonly referred to as an epoxy group, 1,2-epoxide,or oxirane. Preferred epoxy resins are diglycidyl ethers, triglycidylethers, tetraglycidyl ethers, as well as multifunctional glycidyl etherswith more than four epoxy rings which, in the reacting glycerol orpolyol medium, result in the formation of higher molecular weightpolyethercyclicpolyols with substantially improved properties inconnection with drilling fluid performance.

A particularly useful epoxy is a difunctional glycidyl ether such as"EPON 828" (a trademark of Shell Oil Company) which significantlyincreases the number average (M_(n)) molecular weight of a significantfraction of the polyethercyclicpolyols preparation. While not wishing tobe bound by theory, addition of 3 weight percent of "EPON 828" couldresult in doubling the molecular weight of between 10 and 20 percent ofthe preparation. By thus increasing the molecular weight of asignificant portion of the preparation, the copolymerization of "EPON828" results in significantly boosting the M_(w) value of the sample,with attendant significant improvements in the performance of theresulting polyethercyclicpolyols polymer/polyethercyclicpolyolsdiglycidyl ether copolymer mixture.

In order to obtain polyethercyclicpolyols with maximum coveragepotential, it is suitable to use tri- and tetraglycidyl ethers whichwill direct polymerization along more than one direction in a planarconfiguration. It is theorized, although the invention is not limited bythis theory, that the use of such epoxies facilitates the coverage ofopenings in the clay surface of an oil well through which water canenter the clay. While Applicants do not wish to be bound by theory, itis believed that molecules which are substantially planar in structureare most useful with the invention when it is employed as part of adrilling fluid additive. Additionally, the attachment of severalpolyethercyclicpolyols onto the same central molecule of polyglycidylether, allows multiple coordination of cationic species to occur throughthe electron donating oxygen atoms in the ether linkages, which resultsin formation of large molecular aggregates that can inhibit themigration of water molecules from the aqueous phase of the water-baseddrilling mud onto the hydrophilic clay solids of the formation.Water-based drilling muds containing polyethercyclicpolyols actessentially in a manner similar to that of oil-based muds. This theory,of course, is not limiting of the application of this invention.

Experimental results have shown that the impact of using multifunctionalglycidyl ethers on the values of M_(w) and on the performance,particularly as regards swelling of clays when the epoxy-containingpolyols are used as a drilling fluid additive, is truly significant.Thus, when using 3 weight percent "EPON 828" and 3 weight percent "EPON1031" (trade names of Shell Oil Company), the M_(w) values arecorrespondingly 78,015 and 151,000, and the swelling inhibition is thehighest with "EPON 1031", with good performance also observed oninhibition of fluid loss and dispersion.

Although the observation of bimodal distribution of molecular weights inGPC (three-column chromatography) does not require the presence ofepoxies, nevertheless, incorporation of epoxies into thepolyethercyclicpolyols structure has a significant impact on therelative amounts of "large" molecules in the polyethercyclicpolyolproduction, increasing the ratio of large volume molecules/small volumemolecules.

The following epoxies are considered useful in the present invention:

The following epoxies are considered useful in the present invention:##STR2##

With respect to "EPON 828", it is preferred to add the material in aplurality of aliquots, generally two or three aliquots, generallyobserving the layer addition until about 40 to 50 percent of thereaction is complete.

With "EPON 1031", it is suitable to add all the material at thebeginning of the condensation reaction. It is suitable to add a largeramount of "EPON 828" than of "EPON 1031" because of the lower molecularweight of "EPON 828". It is preferred to avoid adding "EPON 828" attemperatures in excess of 270° C., due to risk of prematurepolymerization. The addition of more volatile polyglycidyl ethers mustbe carried out with caution due to their potential toxicity andrelatively higher volatilities.

The epoxy resin can be used in an amount sufficient to give 0.5 to 5weight percent material from the epoxy resin incorporated in the epoxypolyethercyclicpolyol. Alternatively, a relatively high epoxy contentcan be utilized, say 6 to 67, preferably 15 to 40 wt %. Thus, viewed interms of the polyol, the epoxy component content can vary from 0 to 67wt % based on the total weight of the polyol. In utilities where shalestabilization is the primary consideration, high epoxy content ispreferred. In other instances, low epoxy content may be preferred.

The initial pressure can be higher when making the higher epoxy contentpolyols as compared with the initial pressure preferred for the lowepoxy. For instance, the initial pressure can be greater than 180 torr.Generally, the initial pressure will be between 250 and 500, preferably250-350 torr, when the starting polyhydric alcohol component isglycerine. The initial temperature is generally between about 175° and275° C., preferably between 200° and 260° C., more preferably between210° and 250° C. If desired, the reaction can be terminated before 1.07moles of water per mole of polyol are removed. Preferably, thepolyhydric alcohol monomer is introduced into the reaction zone in asingle addition and the epoxy introduced in a plurality of additions,preferably 2 to 10, most preferably 3 to 6 when utilizing the higherepoxy. Generally, if higher epoxy content materials are being produced,more additions are utilized and the addition of the epoxy could becontinuous. With the high epoxy content materials diglycidyl ethers arepreferred instead of tri- and tetraglycidyl ethers.

During the course of the reaction the temperature with the preferredpolyol, glycerol, is generally increased to a range of 250°-300° C.,preferably 251°-280° C., more preferably 260°-273° C. at essentially theinitial pressure. Thereafter, the temperature is increases to 260°-310°C., preferably 261-300. more preferably 280°-287° C. at a pressure ofless than 180, more preferably 40-130mm Hg.

References herein to pressure in terms of mm Hg or torr refer toabsolute pressure, i.e., anything below 760 is a vacuum.

Ethoxylated Propoxylated Alcohols

Another preferred class of the polyalcohols is ethoxylated propoxylatedalcohols of the following general formula

    R[(EO).sub.m -(PO).sub.n ].sub.z OH

where EO=an ethoxy unit

PO=a propoxy unit

R=an alkyl chain of 2-16 carbon atoms, preferably 3-16, most preferably4-10 carbon atoms. At least one of m or n is greater than 0. In theseEO/PO copolymers m and n are variable and the sum of m plus n determinestheir number average molecular weight, which ranges from 500 to 15,000,preferably from 600 to 10,000.

The m/n ratio determines the hydrophobic/hydrophilic balance (HLB),water solubility and nonionic surfactant properties of the copolymer.Solubility depends on the ionic strength of the aqueous medium (higherionic strength results in lower solubility) and temperature. Thetemperature relationship is in a sense an inverse relationship since athigher temperatures the polyalcohols exhibit a cloud point and at lowertemperatures they go back into solution. High temperatures in somesystems has the same effect as high salt solutions.

Polyalcohol Function

Soluble polyalcohols work in a similar way to the salt in that theylower water activity and bind to the clay so as to reduce the amount ofhydration. In addition high molecular weight soluble polyalcohols mayreduce the communication between the formation pore pressure and thehydrostatic pressure due to mud weight. Both mechanisms are advantageousin terms of cuttings stability and actual wellbore stability. Thus, thepolyalcohol, if used, acts in combination with the salt to giveparticularly good shale stabilization.

While Applicants do not wish to be bound by theory, it is believed theinsoluble (essentially insoluble, there is some wetting of the alcohol)alcohols function primarily by a plugging action whereby they preventmud weight/formation pore pressure communication. This is not just asimple mechanical plugging, however. The alcohol groups bind to the claystructure. The combination of soluble and insoluble alcohols results inbetter wetting of the insoluble alcohols and thus better delivery to thepore throats. This is independent of the soluble alcohols beneficialfunctions previously discussed. Also, in systems having both salt andpolyalcohol, the benefits of both are still obtained.

If the pore throats are large enough, the soluble alcohol will bind tothe clay particles in the shale and reduce hydration. The same reactionwill be the reason that the polyalcohol, if used, will enable highsolids tolerance in the drilling fluid. Binding and coating the solids(clays, formation solids and other drilling solids) will lower theparticle to particle interaction which will lower the viscosity.

Again, while not wishing to be bound by theory, applicants believewellbore stability is enhanced when polyalcohols are used because thesoluble polyalcohols form micelles which micelles plug pore entrances.

Thus, density alone does not determine the effectiveness of a drillingfluid in maintaining sufficient pressure to counterbalance the formationpressure. There is also a chemical effect. The cuttings/wellbore (shale)stabilizers described herein, particularly the soluble high molecularweight polyalcohols (if used), insoluble polyalcohols (if used) andethoxylated/propoxylated polyalcohols may lower mud weight pore pressurecommunication so the mean effective stress is not lowered in theformation. Thus, pore pressure is not increased and borehole instabilityis reduced. While not wishing to be bound by theory, it is believed thesoluble alcohol in solution binds water in the drilling fluid whichlowers the water activity of the drilling fluid, i.e., lowers the molarfree energy of the solution. The resulting molar free energy of thewater in the drilling fluid compared with that in the formation resultsin a chemical stabilization of the wellbore by not increasing theformation pore pressure or possibly lowers the pore pressure, thuskeeping the stress state of the wellbore such that it does not exceedthe strength of the formation.

If a polyalcohol and if it is to be only a single polyalcohol, thenpreferably a soluble polyalcohol having a molecular weight in excess of50,000 is used or else an insoluble alcohol having a molecular weight ofless than 10,000 is used.

Alternatively, a mixture of a soluble and an insoluble alcohol can beused. Particularly preferred are mixtures of (a) cyclic polyetherpolyolwhich is water soluble with (b) a cyclic or acyclic polyetherpolyolwhich is insoluble.

Polyethercyclicpolyols having a ratio of x:y within the range of 5:2 to1:10 represent a preferred class of soluble polyethercyclicpolyols.Clearly, the ratio can have many intermediate values such as 3:4 or 2:5(typical). These soluble polyalcohols and mixtures thereof have beenfound to improve interfacial sealing. The insoluble polyol can be anypolyol broadly, or a polyethercyclicpolyol.

Preferred insoluble polyols include polyglycols such as poly(propyleneglycol) of high enough molecular weight to be insoluble.

The polyalcohols such as the polyethercyclicpolyols perform a number ofseparate functions in addition to retardation. They function in thedrilling fluid as a shale stabilizer and fluid loss additive in additionto retarding the setting of the slag during drilling and then in thecementitious slurry they serve as a rheology control agent reducing theincrease in viscosity of the cementitious slurry thus making it morepumpable. While not wishing to be bound by theory, applicants believethe fluid loss prevention comes about indirectly. The polyalcohol has awetting capability and absorbs onto polymers and/or clay in the drillingfluid as noted above and perhaps otherwise modifies the drilling fluid,thus improving the fluid loss capability of the additives in the system.The polyalcohols also tend to improve bonding of the cement to thecasing or liner and to the wellbore.

Fluid Loss Additive

A fluid loss additive is generally selected from synthetic polymers suchas biopolymers, starch, clay, and, as noted hereinabove, polyalcoholssuch as cyclicpolyetherpolyol (which probably acts primarily as anenhancer for the others). Carboxymethyl cellulose can also be usedalthough because of the presence of salt, a higher concentration isneeded (as compared with other polymers) to be effective.

Clay, when used, is generally present in an amount within the range of 2to 50, preferably 5 to 30, more preferably 10 to 20 lbs/bbl of drillingfluid.

Rheology Control

A rheology control agent in the context of a drilling fluid keeps solidsfrom settling out and may be viewed as a viscosifier. The preferredviscosifier for the universal drilling fluid include biopolymers and thesilicates. The silicates, which are essential ingredients in thedrilling fluid used in this invention, also function as boreholestabilizers. Starch can also function, generally in a secondary role, asa viscosifier. The starch, for instance, when used, is generally used inan amount within the range of 2 to 15, preferably 5 to 10 lb/bbl ofdrilling fluid. The biopolymer can be used in an amount within the rangeof about 0.1 to about 3, preferably 0.2 to 1 lbs/bbl of drilling fluid.All of the components, if used, are used in an amount effective toproduce the desired effect, i.e., in this case, a sufficient increase inviscosity so that the mud will carry cuttings up out of the borehole.

Weight Material

The universal drilling fluid must be formulated to have the weightrequired for a particular drilling operation being conducted. This iswell known in the art and in many instances sufficient weight may beprovided by the blast furnace slag. Optionally, however, the weight canbe adjusted using conventional weighting agents such as barite (bariumsulfate). The amount, if any, used would be the amount necessary to givethe desired mud density. Other suitable weighting agents includetitanium oxides such as TiO₂ and iron oxides such as hematite andilmenite.

Shale Stabilizer

This is an optional ingredient. In some formations, the zones beingdrilled do not require stabilization. Also the silicate functions as ashale stabilizer as does lime, if present. Again, the polyalcohol, ifpresent, serves as a shale stabilizer in addition to a retarder.Finally, as noted above, in systems where the aqueous medium contains asalt, the salt acts as a shale stabilizer.

Deflocculant

A deflocculant such as a carbohydrate polymer can be used if needed.Generally, deflocculants, if present, will be used in an amount withinthe range of 0.5 to 10 lbs/bbl of drilling fluid.

Dual Functionality Detail

The following Table summarizes these dual functionality concepts.

                  TABLE A                                                         ______________________________________                                        Function                                                                      Drilling Fluid      Cementitious Slurry                                       Additive                                                                             Primary    Secondary Primary  Secondary                                ______________________________________                                        Water  Cuttings             Hydrating                                                Carrier              Agent                                             Synthetic                                                                            Fluid loss           Fluid loss                                        polymer.sup.1                                                                        control              control                                           Starch.sup.2                                                                         Fluid loss Viscosity Fluid loss                                                                             Viscosity                                       control              control                                           Bio-   Viscosity  Fluid Loss                                                                              Viscosity                                                                              Retarder                                 polymer.sup.3                                                                 Silicate                                                                             Viscosity  Shale     Accelerator                                                                            --                                                         stabilizer                                                  Carboxy-                                                                             Deflocculant                                                                             Retarder  Deflocculant                                                                           Retarder                                 late                                                                          polymer.sup.4                                                                 Barite.sup.5                                                                         Density    --        Density  Solids for                                                                    compressive                                                                   stength                                  Ben-   Fluid loss --        Fluid loss                                                                             Solids for                               tonite.sup.6                                                                         control              control  compressive                                                                   stength                                  Clay/  --         --        Solids   --                                       Quartz                                                                        dust.sup.7                                                                    Slag.sup.8                                                                           Cementitious                                                                             Weight    Cementitious                                                                           Solids                                                     cuttings  agent                                                               stabilizer                                                  Lime.sup.9                                                                           Shale      Alkalinity                                                                              Accelerator                                                                            Solids                                          stabilizer                                                             PECP.sup.10                                                                          Shale      Enhance   Rheology Bond                                     poly-  stabilizer fluid loss                                                                              control  Improver                                 alcohol                                                                              retarder   properties                                                  NaCl   Shale      --        Strength --                                              stabilizer           enhancement                                       ______________________________________                                         .sup.1 A synthetic polymer manufactured by SKW Chemicals Inc. under the       trade name " POLYDRILL", for instance.                                        .sup.2 Starch made by Milpark Inc. under the trade name "PERMALOSE", for      instance.                                                                     .sup.3 "BIOZAN", a biopolymer made by Kelco Oil Field Group, Inc., for        instance. This is a welan gum and is described in U.S. 4,342,866.             .sup.4 A watersoluble carbohydrate polymer manufactured by Grain              Processing Co. under trade name "MORREX", for instance.                       .sup.5 Barite is BASO.sub.4, a drilling fluid weighting agent.                .sup.6 Bentonite is clay or colloidal clay thickening agent.                  .sup.7 A clay/quartz solid dust manufactured by MilWhite Corp. under the      trade name "REVDUST", for instance.                                           .sup.8 Blast furnace slag manufactured by Blue Circle Cement Co. under th     trade name "NEWCEM" is suitable.                                              .sup.9 CaO                                                                    .sup.10 Polycyclicpolyetherpolyol                                        

Functionally, there are four essential and four optional ingredients inthe drilling fluid of this invention, namely,

1) a cuttings carrier,

2) a latent cementitious material

3) a retarder,

4) a rheology control agent (viscosifier), optionally but alwaysprovided by the silicate,

5) generally a fluid loss additive,

6) (optional) a shale stabilizer, and

7) (optional) a weighting agent.

8) (optional) a deflocculant

In functional terms, there are two essential ingredients and severaloptional ingredients in a cementitious slurry, namely,

1) the cementitious or hydratable material itself,

2) hydrating agent,

3) (Optional) accelerator (essential but is provided by action of heatand/or the silicate present in the drilling fluid). Secondaryaccelerators may be added to the cementitious slurry if desired.

4) (Optional) rheology control/thinner (as needed).

5) (Optional) density agent (as needed).

6) (Optional) fluid loss control (will always be carried over from thedrilling fluid),

7) (Optional) a shale stabilizer (as needed). Will generally be carriedover from the drilling fluid,

8) (Optional) solids or aggregate, and

9) (Optional) strength enhancing agents.

As can be seen from the above Table, a composition as simple as onehaving water, blast furnace slag, a silicate and a retarder provides allof the essential and all but one (fluid loss) of the optional drillingfluid functions and all of the essential cementitious functions. This isbecause the water serves as the cuttings carrier in the drilling fluidand the hydrating agent in the cementitious slurry. The blast furnaceslag serves a two-fold function by providing the essential cementitiousfunction and the optional weight function in the drilling fluid andserves the dual function of providing the cementitious material in thecementitious slurry. The silicate serves a two-fold function in thedrilling fluid of viscosifier and modifier of the water activity of theaqueous continuous phase (shale stabilization) in the drilling fluid andthen serves the dual function as an accelerator in the cementitiousslurry. Finally, any of the retarders discussed herein can be used.

Preferably, the universal fluid composition further contains a salt suchas sodium chloride to provide further shale stabilization and strengthenhancement in the cementitious slurry. Similarly, the compositionpreferably contains a fluid loss control agent such as a sulfonatedsynthetic polymer or starch (which also gives viscosity). Also, it maybe preferred in many instances to use a biopolymer to give viscosity.Similarly, lime may be present to further give cuttings/wellborestabilization and to provide alkalinity in the drilling fluid and tofunction as an accelerator and solids in the cementitious slurry.

Almost always a clay such as bentonite or prehydrated bentonite will bepresent which provides fluid loss control in the drilling fluid and inthe cementitious slurry and also solids in the cementitious slurry. Theclay is frequently included in the initial drilling fluid and in anyevent will almost always be encountered during drilling. Frequently,clay, prehydrated in fresh water, is used initially to give thefunctions such as fluid loss control since the clay in a salt waterenvironment does not hydrate readily and thus imparts less viscosity tothe fluid. This is generally referred to as the "yield", i.e., theamount of viscosity imparted by the clay.

If flocculation is a problem in a particular system, a deflocculant suchas a carbohydrate polymer, acrylate polymer, sulfonate polymer, styrenemaleic anhydride polymer, organic acid or polyalcohol can be used whichwill also provide retardation of the blast furnace slag during drillingand act as a deflocculant in a cementitious slurry.

Finally, if additional weight is desired in the drilling fluid, this canbe provided with a weighting agent such as barite or bentonite whichwill also give solids and weight to the cementitious slurry.

The clay/quartz dust is shown in Table A and was used in laboratorytests of drilling fluids to simulate drill solids produced in actualdrilling, and thus would not generally be added to an actual drillingfluid.

While the ingredients can be added in any order, there are twocombinations where a significant improvement flows from the additionsequence. First, if a biopolymer and lime are used, the biopolymershould be added after the lime. This gives better yield, i.e., enhancesviscosity imparted and fluid loss prevention capabilities. Second,polymers such as starch and biopolymers should be added before thepolyalcohol to allow the polymers to hydrate before contact with thepolyalcohol. This gives better hydration and thus better polymerextension (swelling).

Unlike Portland cement which is incompatible with ingredients which areinvariably in drilling fluids, blast furnace slag is compatible withdrilling fluids. This is shown in Hale and Cowan, referred tohereinabove. Thus, blast furnace slag can simply be added to anyconventional drilling mud to give a drilling composition which canthereafter be set through the action of an activator as in thisinvention. Such systems are entirely operable and represent an advancein the art. However, while compatible with drilling fluids, blastfurnace slag tends to deactivate the function of certain ingredientscommon in drilling fluids. For instance, drilling fluids can containpartially hydrolyzed polyacrylamide as a shale stabilizer andsecondarily as a viscosifying agent. Blast furnace slag, whilecompatible, tends to reduce the function of the partially hydrolyzedpolyacrylamide, thus resulting in the partial waste of an ingredient.Also, in systems not employing lime, blast furnace slag tends to reducefluid loss control. These adverse effects are probably the result of thecalcium level, and the pH imparted by the blast furnace slag whichadversely impacts the most common shale stabilizer, partially hydrolyzedpolyacrylamide and adversely affects fluid loss control. The calcium andhigh pH flocs the solids in non-lime systems and thus good filter cakequality is not produced. Thus, the use of a lime based system providesthe optimum base fluid for implementation of blast furnace slag in auniversal fluid. Silicate muds also give advantages with blast furnaceslag similar to those obtained with lime muds.

Activation

The drilling can be carried out for any period of time desired with thesame drilling fluid (augmented with fresh fluid to compensate for lossand greater hole depth) without the blast furnace slag setting. Forinstance, the drilling can be carried out for one day up to any timeneeded, generally between greater than one day and 100 days. Then onactivation the blast furnace slag will set to give its full potential ofcompressive strength.

In its simplest form, activation may occur simply through an increase intemperature and/or the effect of residual silicate. For instance, duringdrilling the circulation of the drilling fluid has as one of itsfunctions the carrying off of generated heat and any heat from theformation. Thus, during the drilling the retarders in the drilling fluidinhibit hydration of the blast furnace slag as does the circulationitself. On cessation of drilling and displacement of the drilling fluidsselectively into the area to be cemented, the temperature will rise inthose systems where the circulation was carrying off heat from theformation to a degree sufficient to set the cementitious slurry.

In most instances, however, an activator system will be added to thedrilling fluid between the drilling operation and the cementingoperation. The activator system can be simply additional blast furnaceslag and, in any event, additional blast furnace slag will generally beincorporated. Also, other ingredients which are, or which may be,present in the drilling fluid and which have an accelerator function canbe added in additional quantities between the drilling and thecementing. For instance, additional silicate can be added or if thedrilling fluid has lime, i.e., is a lime mud, additional lime can beadded.

Suitable activators which are generally not a part of the drillingfluid, but are added between the drilling operation and the cementingoperation, include lithium hydroxide, lithium carbonate, sodiumfluoride, sodium silicofluoride, magnesium hydroxide, magnesium oxide,magnesium silicofluoride, zinc carbonate, zinc silicofluoride, zincoxide, sodium carbonate, sodium bicarbonate, titanium carbonate,potassium carbonate, potassium bicarbonate, sodium hydroxide, potassiumhydroxide, potassium sulfate, potassium nitrite, sodium or potassiumaluminate, potassium nitrate, calcium hydroxide, sodium sulfate, coppersulfate, calcium oxide, calcium sulfate, calcium nitrate, calciumnitrite, and mixtures thereof. A mixture of caustic soda (sodiumhydroxide) and soda ash (sodium carbonate) is preferred because of theeffectiveness and ready availability. When mixtures of alkaline agentssuch as caustic soda and soda ash are used the ratio can vary ratherwidely since each will function as an accelerator alone. Preferably,about 1 to 20 lbs/bbl of caustic soda, more preferably 2 to 6 lbs/bbl ofcaustic soda are used in conjunction with from 2 to 50 lbs/bbl,preferably 2 to 20 lbs/bbl of soda ash. Generally, 2 to 70 lbs/bbl oftotal activator is used. The references to "lbs/bbl" means pounds perbarrel of final cementitious slurry.

In some instances, it may be desirable to use a material for aparticular effect along with the activator even though it may also actas a retarder. For instance, a chromium lignosulfonate may be used as athinner in the cementitious slurry along with the activator even thoughit also functions as a retarder.

Other suitable thinners include chrome-free lignosulfonate, lignite,sulfonated lignite, sulfonated styrene maleic-anhydride, sulfomethylatedhumic acid, naphthalene sulfonate, a blend of polyacrylate andpolymethacrylate, an acrylamideacrylic acid copolymer, phenol sulfonate,dodecylbenzene sulfonate, sulfomethylated tree extract, stearyl amineand lauryl amine surfactants, sulfonated styrene-toluene copolymers, andmixtures thereof.

In accordance with this invention the drilling process is carried out asdescribed hereinabove with the universal fluid to produce a boreholethrough a plurality of strata, thus laying down a filter cake. Becausethe filter cake comprises blast furnace slag, it will eventually hydratewith time to produce a solid. This hydration is further accelerated bymigration of activators from the cementitious slurry when it isdisplaced into the annulus between a pipe and the borehole wall on whichthe filter cake is laid down. Furthermore, because the cementitiousslurry is compatible with the drilling fluid, a good bond will beobtained between the cementitious slurry and the borehole wall. Further,the cementitious slurry is compatible with any mud which is not removedduring displacement. Thus:

a) drilling filter cake deposited while drilling through permeable zoneswill be converted into an effective sealant;

b) whole mud that has not been removed from washed out sections of thehole during displacement will harden with time and, therefore, providean effective sealant and lateral support to the casing.

Filter Cake Setting

In yet another embodiment of this invention the drilling process iscarried out as described hereinabove with the universal fluid to producethe borehole through a plurality of strata thus laying down the filtercake. Prior to the cementing operation, an activator is passed intocontact with the filter cake, for instance by displacing out thedrilling fluid and circulating a fluid containing the activator down thedrill string and up the annulus between the drill string and the filtercake, or else the drill string is removed and the casing inserted andthe activator circulated down the casing and up the annulus (or down theannulus and up the drill string or casing). Preferably, the circulationis carried out by using the drill string, this being one benefit of thisembodiment of the invention whereby the filter cake can be "set" to shutoff gas zones, water loss, or to shut off lost circulation in order tokeep drilling without having to remove the drill string and set anotherstring of casing. Alternatively, the activator can be added to thedrilling fluid instead of using a separate fluid. This filter cakesetting can also be used to stabilize zones which may be easilywashed-out (salt zones wherein the salt is soluble in water, forinstance) or other unstable zones. After the drilling is complete, thedrill string is removed, and the cementing carried out.

Conventional spacers may be used in the above described sequence. Also,any leftover fluid having activators therein may be displaced out of theborehole by the next fluid and/or a spacer fluid and stored forsubsequent use or disposal.

In this embodiment where the filter cake is "set", the activator can beany of the alkaline activators referred to hereinabove such as a mixtureof sodium hydroxide and sodium carbonate.

Lime

As previously noted, preferred systems contain lime. These systems thusare analogous to conventional drilling fluids known as high lime, lowlime, and low lime/salt/alcohol. By "low lime" is meant a drilling fluidhaving about 0.5 to 3, generally 0.5 to 2.0 lbs of unreacted lime perbarrel of drilling fluid. By "high lime" is meant a drilling fluidhaving from greater than 3.0 to 15 lbs of unreacted lime per barrel ofdrilling fluid. The low lime/salt/alcohol fluids have about 1 to 4.0lbs/bbl of unreacted lime, about 18 to 109 lbs/bbl of salt such assodium chloride, and about 1 to 168 lbs/bbl, preferably 10 to 80lbs/bbl, more preferably 15 to 65 lbs/bbl, most preferably 40 to 60lbs/bbl of a polyhydric alcohol per barrel of drilling fluid.

Ingredient Ratios

Blast furnace slag is present in the drilling fluid (universal fluid) inan amount within the range of about 1 to about 100 lbs/bbl of finaldrilling fluid, preferably 10 to 80 lbs/bbl, most preferably 20 to 50lbs/bbl. As noted above, additional blast furnace slag is generallyadded between the drilling operation and the cementing operation to givea total concentration of blast furnace slag in the cementitious slurrywithin the range of from about 20 to 600 lbs/bbl, preferably 100 to 500lbs/bbl, most preferably 150 to 300 lbs/bbl.

The silicate is generally present in an amount within the range of 1 to100, preferably 2 to 15, most preferably 5 to 10 lbs/bbl based onbarrels of drilling fluid.

The concentration of the polyalcohol, if used, in the water phase of theuniversal fluid of this invention will generally be 1-50% by volume andpreferably from about 3 to 30% by volume based on the volume of water,more preferably from 5 to 25% by volume, most preferably between 10 and20% by volume. The soluble:insoluble polyols can be used in weightratios of about 0.1:1 to 10:1, preferably 0.25:1 to 2:1, more preferably0.5:1 to 1:1 soluble:insoluble.

Dilution

Another feature of this invention is the ability to tailor the rheologyof both the drilling fluid and the final cement to the conditions of aparticular wellbore. This results in part from the fact that the use ofslag as the hydraulic material gives a final cementitious slurry whichis not weakened in the manner that would be the case with Portlandcement if the slurry is more dilute. On the other hand, additional slagdoes not impart extremely high viscosity to the slurry and thus a higherconcentration of hydraulic material can be used if desired.

However, in the preferred method of this invention, the drilling fluidis utilized and thereafter diluted prior to or during the addition ofadditional blast furnace slag. The dilution fluid can be the same as theliquid used to make the drilling fluid or it can be different.Generally, it will be brine, especially if the drilling fluid was madeusing brine. It can also be a more concentrated brine. In manyinstances, it is preferred that both the dilution fluid and the originalliquid used to produce the initial drilling fluid be seawater. This isespecially beneficial in offshore drilling applications where freshwater is not readily available and seawater is.

Thus, a significant improvement in the operating procedure is provided.This is because the density of the drilling fluid can be chosen in thefirst place to be sufficient to avoid inflow into the wellbore becauseof formation pressure but insufficient to rupture the wellbore wall andforce fluid out into the formation. By utilizing the dilution andthereafter the addition of additional blast furnace slag, thecementitious slurry can also have the density tailored to the particularoperation the same as the drilling fluid.

The dilution can be carried out in either of two ways. First, a vesselcontaining drilling fluid can simply be isolated and the desired amountof water or other diluent added thereto. In a preferred embodiment,however, the drilling fluid is passed to a mixing zone as a flowingstream and the diluent added to the flowing stream. Thereafter, theadditional blast furnace slag is added. This avoids highly viscouscementitious slurry compositions and allows all of the pumping to bedone with piping and pumps associated with the well rig without the needfor pumps designed for pumping cement. This is of particular value inthe areas to which this invention is of special utility, offshoredrilling rigs where the transportation of additional pumping equipmentis particularly inconvenient. Thus, it is possible to tailor the finaldensity of the cementitious slurry, if desired, to a value within therange of 30% less to 70% more than the original density of the drillingfluid, preferably within the range of 15% less to 50% more, mostpreferably essentially the same, i.e., varying by no more than ±5 weightpercent.

Displacement

Conventional displacement techniques can be used to displace theuniversal fluid of this invention with the cementitious slurry. However,because of the inherent compatibility of the drilling fluid and thecementitious slurry, wiper plugs and spacer fluids can be omitted. Thusthe cementitious slurry can be placed in direct fluid contact with thedrilling fluid and the drilling fluid displaced out of the annulusbetween a pipe being cemented and a surrounding wall. The cement is, inturn, displaced to a preselected location in the annulus by direct fluidcontact with a displacement fluid such as seawater or drilling fluid.

Generally, this involves introducing a cementitious slurry into a casingor liner followed by the displacement fluid and displacing thecementitious slurry down the casing or liner and back up into theannulus surrounding the casing or liner.

EXAMPLE 1

This example is presented to show the drilling fluid characteristics andcementitious characteristics of compositions in accordance with theinvention.

    __________________________________________________________________________    DATA FOR 11.5 ppg MUDS                                                                      SLNP                                                                              SENP                                                                              SNP SLNP                                                                              SENP                                                                              SNP SLNP                                                                              SENP                                                                              SNP                             __________________________________________________________________________    Density 11.5 lb/gal                                                           23% NaCl brine (bbl)                                                                        0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8                             Lime (lb/bbl) 4   --  --  4   --  --  4   --  --                              "NEWCEM.sup.1 " (lb/bbl)                                                                    60  60  60  40  40  40  30  30  30                              "MOR-REX.sup.2 " (lb/bbl)                                                                   4   4   4   4   4   4   4   4   4                               Starch (lb/bbl)                                                                             6   6   6   6   6   6   6   6   6                               "POLYDRILL.sup.3 " (lb/bbl)                                                                 6   6   6   6   6   6   6   6   6                               "FILTREX.sup.4 " (lb/bbl)                                                                   --  --  --  --  --  --  --  --  --                              Silicate (lb/bbl)                                                                           --  5   --  --  5   --  --  5   --                              Bentonite (lb/bbl)                                                                          20  20  20  20  20  20  20  20  20                              "REVDUST.sup.5 " (lb/bbl)                                                                   25  25  25  25  25  25  25  25  25                              "BIOZAN.sup.6 " (lb/bbl)                                                                    0.5 --  0.4 0.5 --  0.4 0.5 --  0.4                             Barite (lb/bbl)                                                                             71  71  71  71  71  71  71  71  71                              PECP.sup.7 (lb/bbl)                                                                         36  36  36  36  36  36  36  36  36                              16 hours Hot Roll                                                             600 rpm       50.sup.1A                                                                         71  49  51  71  49  --  --  --                              300 rpm       29  40  28  31  41  29  --  --  --                              200 rpm       21  30  21  20  31  20  --  --  --                              100 rpm       13  18  14  12  18  13  --  --  --                              6 rpm         3   6   3   3   5   3   --  --  --                              3 rpm         2   5   3   2   5   2   --  --  --                              Plastic Viscosity (cp)                                                                      21  31  21  20  30  20  --  --  --                              Yield Point (lb/100 ft.sup. 2)                                                              8   9   7   11  11  9   --  --  --                              Gel Strength - 10 second                                                                    3   4   2   3   3   1   --  --  --                              Gel Strength - 10 minute                                                                    6   8   5   7   9   5   --  --  --                              HPHT.sup.8 (mls)                                                                            7.8 6.8 8.4 8.6 8   8.6 --  --  --                              HPHT (cake thickness,                                                                       3   3   3   3   3   3   --  --  --                              32nd inch)                                                                    60 hours-Axial                                                                              123 105 95  47  38  30  12  8   5                               Compressive Strength                                                          (psi)                                                                         650 hours Density (11.5 ppg)                                                  600 rpm       46.sup.1B                                                                         64  52  44  61  50  --  --  --                              300 rpm       26  35  28  25  33  30  --  --  --                              200 rpm       17  25  21  18  24  19  --  --  --                              100 rpm       9   15  12  10  13  12  --  --  --                              6 rpm         2   3   3   2   3   2   --  --  --                              3 rpm         1   2   2   1   2   2   --  --  --                              Plastic Viscosity (cp)                                                                      20  29  24  19  28  20  --  --  --                              Yield Point (lb/100 ft.sup.2)                                                               6   6   4   6   5   10  --  --  --                              Gel Strength - 10 second                                                                    2   3   1   2   3   2   --  --  --                              Gel Strength - 10 minute                                                                    3   6   4   4   5   5   --  --  --                              HPHT (mls)    11.5                                                                              10.6                                                                              9.6 9.8 11  10.5                                                                              --  --  --                              HPHT (cake thickness,                                                                       3   3   3   3   3   3   --  --  --                              32nd inch)                                                                    60 hours-Axial                                                                              131 102 90  51  42  32  12  8   5                               Compressive Strength                                                          (psi)                                                                         __________________________________________________________________________     .sup.1 Trade name of Blue Circle Cement Co. for blast furnace slag having     a Blaine specific surface area of about 5,500 cm.sup.2 /g                     .sup.2 Trade name of Grain Processing Company for a water soluble             carbohydrate polymer                                                          .sup.3 Trade name of SKW Chemicals, Inc. for a synthetic polymer              .sup.4 Trade name of Milpark for polyanionic lignin resin                     .sup.5 Trade name of clay/quartz dust manufactured by Milwhite Corporatio     .sup.6 Trade name of Kelco Oil Field Group Inc. for welan gum biopolymer,     described in more detail in U.S. 4,342,866, the disclosure of which is        hereby incorporated by reference                                              .sup.7 Polycyclicpolyetherpolyol                                              .sup.8 High pressure, high temperature                                        .sup.1A Viscosity reading from Fann 35 viscometer at indicated rpm after      the hot rolling at 120° F.                                             .sup.1B Viscosity reading from Fann 35 viscometer at indicated rpm after      650 hours rolling at 150° F.                                      

In this Example "S" represents salt (NaCl), "L" represents lime; "N"represents blast furnace slag; "P" represents polyalcohol, specificallya polycyclicpolyetherpolyol; and "E" represents sodium silicate. Thedesignation "HPHT (mls)" represents high pressure high temperature fluidloss. The corresponding reference to cake thickness represents the highpressure high temperature filter cake thickness.

As can be seen from the rheology data, particularly the low plasticviscosity numbers, all three of the compositions described have gooddrilling fluid characteristics so far as theology is concerned. The highpressure high temperature fluid loss data show that they all have gooddrilling fluid characteristics from this very important standpoint. The60-hour compressive strength data shows that with as little as 40lbs/bbl of blast furnace slag the drilling fluid itself has sufficientstrength on setting to provide some lateral support to the casing orliner. This is significant in that filter cake will harden and providebetter seal. It is also significant in that if an insufficient amount ofcementitious slurry is introduced during primary cementing, any drillingfluid in an annulus to be cemented will eventually set and provide somelateral support. This is quite significant. Even if no error is made incalculating the amount of cementitious slurry needed, an insufficientamount may still be introduced because of the unknown amounts that maybe lost to wash-outs in the formation or otherwise lost. The 650 hourdata show the system lasted for a long time as a drilling fluid andthereafter was still capable of being converted to a set cement.

EXAMPLE 2

The following example shows the same good results with a higher densitydrilling fluid made in accordance with the invention. The viscosity datais from a Fann 35 viscometer as in Example 1.

    __________________________________________________________________________    DATA FOR 14.0 ppg MUDS                                                                      SLNP                                                                              SLNP                                                                              SENP                                                                              SNP SLNP                                                                              SLNP                                                                              SENP                                                                              SNP SLNP                                                                              SLNP                                                                              SENP                                                                              SNP                 __________________________________________________________________________    23% NaCl brine (bbl)                                                                        0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                                                                              0.73                Lime (lb/bbl) 4   4   --  --  4   4   --  --  4   4   --  --                  "NEWCEM.sup.1 " (lb/bbl)                                                                    60  60  60  60  40  40  40  40  20  20  20  20                  "MOR-REX.sup.2 " (lb/bbl)                                                                   4   4   4   4   4   4   4   4   4   4   4   4                   Starch (lb/bbl)                                                                             6   6   6   6   6   6   6   6   6   6   6   6                   "POLYDRILL.sup.3 " (lb/bbl)                                                                 6   --  6   6   6   --  6   6   6   --  6   6                   "FILTREX.sup.4 " (lb/bbl)                                                                   --  6   --  --  --  6   --  --  --  6   --  --                  Silicate (lb/bbl)                                                                           --  --  5   --  --  --  5   --  --  --  5   --                  Bentonite (lb/bbl)                                                                          20  20  20  20  20  20  20  20  20  20  20  20                  "REVDUST.sup.5 " (lb/bbl)                                                                   25  25  25  25  25  25  25  25  25  25  25  25                  "BIOZAN.sup.6 " (lb/bbl)                                                                    0.5 0.75                                                                              --  0.4 0.5 0.75                                                                              --  0.5 0.5     --  0.5                 Barite (lb/bbl)                                                                             216 216 216 216 216 216 216 216 216 216 216 216                 PECP.sup.7 (lb/bbl)                                                                         32  32  32  32  32  32  32  32  32  32  32  32                  16 hours Hot Roll                                                             (Density 14 ppg)                                                              600 rpm       50  61  105 132 48  58  111 140 46  57  106 135                 300 rpm       29  36  63  81  27  35  66  87  25  33  65  85                  200 rpm       21  27  46  62  20  25  48  66  19  24  46  65                  100 rpm       13  16  31  38  12  15  30  42  11  14  28  41                  6 rpm         3   5   7   11  1   4   9   15  1   2   8   13                  3 rpm         2   3   6   4   2   3   8   5   1   2   7   4                   Plastic Viscosity (cp)                                                                      21  25  42  51  21  23  45  53  21  24  41  50                  Yield Point (lb/100 ft.sup.2)                                                               8   11  21  30  6   12  21  34  4   9   24  35                  Gel Strength - 10 second                                                                    3   5   4   5   4   6   8   6   3   5   8   6                   Gel Strength - 10 minute                                                                    6   11  13  14  7   12  18  16  7   11  16  14                  HPHT.sup.8 (mls)                                                                            2.4 6.2 9.2 4   2.4 6.2 9.2 4   7.9 9   8.7 8.5                 HPHT (cake thickness,                                                                       3   3   3   3   3   3   3   3   3   3   3   3                   32nd inch)                                                                    60 hours-Axial                                                                              250 274 220 145 132 115 87  76  47  43  13  10                  Compressive Strength                                                          (psi)                                                                         650 hours - Density (14 ppg)                                                  600 rpm       47  55  70  117 45  51  63  92  43  50  58  87                  300 rpm       26  30  38  66  24  29  34  53  22  27  33  51                  200 rpm       18  21  28  47  17  19  24  39  16  18  22  38                  100 rpm       10  12  15  28  9   10  13  23  8   9   11  22                  6 rpm         2   3   3   8   2   4   2   10  3   4   3   8                   3 rpm         1   2   2   4   1   3   1   5   4   2   1   4                   Plastic Viscosity (cp)                                                                      21  25  32  51  21  22  29  39  21  23  25  36                  Yield Point (lb/100 ft.sup.2)                                                               5   5   6   15  3   7   5   14  1   4   8   15                  Gel Strength - 10 second                                                                    2   2   3   0.8 2   3   2   3   2   3   2   4                   Gel Strength - 10 minute                                                                    3   7   6   13  3   8   4   12  4   5   3   9                   HPHT (mls)    8.9 9.4 9.4 10.5                                                                              10  9.6 9.2 8.8 9.8 8.4 9.4 11                  HPHT (cake thickness,                                                                       3   3   3   3   3   3   3   3   3   3   3   3                   32nd inch)                                                                    60 hours-Axial                                                                              286 245 211 162 127 121 88  81  42  53  15  10                  Compressive Strength                                                          (psi)                                                                         __________________________________________________________________________     .sup.1 Trade name of Blue Circle Cement Co. for blast furnace slag having     a Blaine specific surface area of about 5,500 cm.sup.2 /g                     .sup.viscometer name of Grain Processing Company for a water soluble          carbohydrate polymer                                                          .sup.3 Trade name of SKW Chemicals, Inc. for a synthetic polymer              .sup.4 Trade name of Milpark for polyanionic lignin resin                     .sup.5 Trade name of clay/quartz dust manufactured by Milwhite Corporatio     .sup.6 Trade name of Kelco Oil Field Group Inc. for welan gum biopolymer,     described in more detail in U.S. 4,342,866, the disclosure of which is        hereby incorporated by reference                                              .sup.7 Polycyclicpolyetherpolyol                                              .sup.8 High pressure, high temperature                                   

EXAMPLE 3

This Example is presented to correlate the amount of blast furnace slagin a universal drilling fluid with strength development when anactivator is utilized (as would occur from migration of the activatorfrom a blast furnace slag cementitious slurry or from the circulation ofan activator or from the circulation of an activator-containing drillingfluid prior to the introduction of the cementitious slurry). The resultsare shown for three of the systems of the type set out in Examples 1 and2, namely, SNP, SENP (lime being part of the activator system) and SLNP.

    __________________________________________________________________________    EXAMPLE 3                                                                     Salt/NewCem/PECP = SNP                                                        Salt/Econolite/Newcem/PECP = SENP                                             Salt/Lime/NewCem/PECP = SLNP                                                  Axial Compressive Strength                                                                            Time (hours)                                                           NEWCEM.sup.1                                                                         12   24   48   330                                    14 ppg           (lb/bbl)                                                                             (150° F.)                                                                   (150° F.)                                                                   (150° F.)                                                                   (75°)                           __________________________________________________________________________    Salt/"NEWCEM"/"PECP.sup.2 "                                                                    10     0     0    0   --                                     with             10     0     0    0   --                                     Soda Ash (5 lb/bbl)                                                                            20     0     5    9   --                                     NaOH (10 lb/bbl) 20     0     5   10   --                                                      30     5    25   37   --                                                      30     5    24   36   --                                                      40     10   45   62    76                                                     40     14   57   77    80                                                     60     32   113  145  162                                                     60     36   125  160  175                                    Salt/"ECONOLITE.sup.3"/                                                                        10     0     0    0   --                                     "NEWCEM"/PECP with                                                                             10     0     0    0   --                                     Lime (5 lb/bbl)  20     0     6   11   --                                     NaOH (10 lb/bbl) 20     0     6   12   --                                                      30     7    32   46   --                                                      30     7    33   48   --                                                      40     14   32   84    82                                                     40     12   33   89    71                                                     60     47   156  196  184                                                     60     50   164  205  201                                    Salt/Lime/"NEWCEM"/"PECP"                                                                      10     0     3    8   --                                     with             10     0     3    7   --                                     Soda Ash (5 lb/bbl)                                                                            20     6    23   47   --                                     NaOH (10 lb/bbl) 20     5    18   38   --                                                      30     15   44   84   --                                                      30     17   50   92   --                                                      40     24   69   123  132                                                     40     26   75   132  134                                                     60     53   136  226  251                                                     60     55   139  230  223                                    __________________________________________________________________________     .sup.1 Trade name of Blue Circle Cement Co. for blast furnace slag having     a Blaine specific surface area of about 5,500 cm.sup.2 /g                     .sup.2 Trade name of Grain Processing Company for a water soluble             carbohydrate polymer                                                          .sup.3 Trade name of Halliburton for sodium silicate                     

The data show two things. First, it is shown that with an activator,some axial compressive strength is attained even at room temperature.This shows that the drilling mud itself can provide support to a casingor liner if insufficient cementitious slurry is introduced due to lossfrom wash-outs or other unforeseen causes. Second, it shows that aminimum of 30 to 60 lbs of blast furnace slag per barrel of universaldrilling fluid is necessary to give good results, although in fact theeffect in actual use is more dramatic because even at lowerconcentrations, the blast furnace slag is concentrated in the filtercake and activators can easily migrate into it or be circulated intocontact with it.

EXAMPLE 4

In this Example, shale cuttings having a size of 10 mesh are put in aroll mill with a liquid having the ingredients listed in the heading ofeach column. For example, in the first column, the 10 mesh shale isrolled for the indicated time at 150° F. At each time indicated analiquot is taken and the percent of shale that will still be retained ona 10 mesh screen is indicated. The last row shows the results of takinga portion of the 110 aliquot and rolling it for 8 hours in fresh water(a stringent test of the degree of shale stabilization).

    __________________________________________________________________________    Hot Rolling Dispersion Tests                                                              1    2   3    4  5   6   7  8   9   10                                        Control                                                                            PHPA                                                                              PHPA/N                                                                             SLP                                                                              SLNP                                                                              SENP                                                                              SNP                                                                              SLNP                                                                              SENP                                                                              SNP                           __________________________________________________________________________    23% NaCl brine (bbl)                                                                      0.73 0.73                                                                              0.73 0.73                                                                             0.73                                                                              0.73                                                                              0.73                                                                             0.73                                                                              0.73                                                                              0.73                          Lime (lbs/bbl)                                                                            --   --  --   4  4   --  -- 4   --  --                            "NEWCEM.sup.1 " (lbs/bbl)                                                                 --   --  40   -- 40  40  40 20  20  20                            Silicate (lbs/bbl)                                                                        --   --  --   -- --  5   -- --  --  --                            "PECP.sup.2 " (lbs/bbl)                                                                   --   --  --   32 32  32  32 32  32  32                            PHPA.sup.3  --   0.15                                                                              0.15 -- --  --  -- --  --  --                            Rolling Time (Hours)                                                                      10 Mesh Shale Cuttings                                             25         61.4 78.9                                                                              80.4 97.4                                                                             94.7                                                                              86.9                                                                              93.4                                                                             93.5                                                                              86  92.2                           50         25.6 59.7                                                                              71.2 94.7                                                                             91.1                                                                              76.2                                                                              88.2                                                                             89.9                                                                              75.6                                                                              86.3                          110         8.4  29.7                                                                              42.1 90.4                                                                             82.9                                                                              43.3                                                                              77.4                                                                             81.2                                                                              42.1                                                                              76.2                          167         3.2  13.4                                                                              26.6 84.4                                                                             78.9                                                                              25.6                                                                              73.3                                                                             77.6                                                                              25  71.4                          196         0.5  8.8 16.8 83.4                                                                             77.4                                                                              19.4                                                                              70.1                                                                             73.1                                                                              19.4                                                                              68.4                          263         0    3.6 11.2 82.4                                                                             76.6                                                                              16.8                                                                              67.1                                                                             74.5                                                                              14.8                                                                              64.8                          8 Hr Fresh Water                                                                          0    0   0    86.4                                                                             76.6                                                                              34.5                                                                              68.5                                                                             --  --  --                            After 110 Hours                                                               __________________________________________________________________________     .sup.1 Trade name of Blue Circle Cement Co. for blast furnace slag having     a Blaine specific surface area of about 5,500 cm.sup.2 /g                     .sup.2 Trade name of Grain Processing Company for a water soluble             carbohydrate polymer                                                          .sup.3 Partially hydrolyzed polyacrylamide                               

As can be seen, a drilling fluid made up of only salt and water(column 1) gives so little stabilization that after 263 hours none ofthe shale is left intact. With PHPA, the industry standard drillingfluid shale stabilizer, only 3.6 percent is intact (column 2) and, asshown in Column 10, after 8 hours of hot rolling in fresh water at 150°F., it is believed none remains although it was not measured. Freshwater is a good test medium for shale stability since fresh water ismore active in destabilizing shale than is salt water. Column 3 showsthat PHPA is also ineffective in the presence of blast furnace slag.Columns 6 and 9 show that all of the compositions used in this inventionare effective shale stabilizers even under the very severe conditions ofthese tests; all had at least some shale intact even after 263 hours.Also in the invention compositions tested (column 6) a significantamount of shale survived both the 110 hours hot rolling and the 8 hoursin fresh water. The comparison run of column 4 simply shows that thebeneficial effects of blast furnace slag (settable filter cake, forinstance) can be obtained without destroying the shale stabilizingeffect of the polyalcohol.

In the following second part of this Example, the compositions ofcolumns 1-7 (labeled here 3-9) and two additional compositions werecontacted with Pierre test cores at 150° F. for 185 hours. The resultswere as follows:

    __________________________________________________________________________                1    2   3    4   5    6  7   8   9                                           Native.sup.4                                                                       NaCl                                                                              Control                                                                            PHPA                                                                              PHPA/N                                                                             SLP                                                                              SLNP                                                                              SENP                                                                              SNP                             __________________________________________________________________________    NaOH, lbs/bbl                                                                             --    4   0    4   4     4                                                                                4   4   4                             Universal Compressive                                                                     633  864 655  604 611  1236                                                                             1289                                                                              1025                                                                              1358                            Strength, psi                                                                 __________________________________________________________________________     .sup.4 "Native" means untreated core                                     

This data shows a remarkable improvement in Pierre test cores inaccordance with the invention (Run 8) compared with the industrystandard shale stabilizer, PHPA (Run 4).

EXAMPLE 5

This Example shows the effect of using a mixture of soluble andinsoluble alcohols. The soluble alcohol is a polycyclicpolyetherpolyolof the type shown herein, wherein average x=2.0 and average y=5.0. Theinsoluble alcohol is a poly(propylene glycol) of high enough weight tobe insoluble. It is a material sold by Dow Chemical Company under thetrade name "PG 4000".

The base mud with which the listed composition was combined was asfollows:

20 lbs/bbl bentonite gel

25 lbs/bbl drill solids¹

3 lbs/bbl starch

3 lbs/bbl synthetic polymer²

4 lbs/bbl "MOR-REX"³

0.5 lbs/bbl "BIOZAN"⁴

The salt in each instance was used in an amount of 20 wt % based on theweight of the continuous phase. The lime was used in an amount of 4lbs/bbl of drilling fluid.

    __________________________________________________________________________                             Predicted                                                                     Additive                                                                           Actual                                                       Percent.sup.1                                                                             Response                                                                           Response                                                                           Percent                                    Mud Additive System                                                                        Alcohol                                                                            HPHT.sup.2 (mls)                                                                     (mls)                                                                              (mls)                                                                              Increase                                   __________________________________________________________________________    Salt/Lime Control                                                                          0    14                                                          Salt/Lime Polypropylene                                                                    14.9 12                                                          Glycol                                                                        Salt/Lime "PECP"                                                                           6.7  10.8                                                        Salt/Lime/"PECP"/PG                                                                        6.7/14.9                                                                           5.6    8.8  5.6  57.1                                       + 40 lb/bbl Slag                                                                           0    16                                                          Salt/Lime Control                                                             Salt/Lime Polypropylene                                                                    14.9 14.2                                                        Glycol                                                                        Salt/Lime "PECP"                                                                           6.7  11.5                                                        Salt/Lime/"PECP"/PG                                                                        6.7/14.9                                                                           8.7    9.7  8.7  11.5                                       + 40 lb/bbl Slag                                                                           0    15                                                          Salt/Lime Control                                                             Salt/Lime Polypropylene                                                                     8.75                                                                              15.5                                                        Glycol                                                                        Salt/Lime "PECP"                                                                            8.75                                                                              9                                                           Salt/Lime/"PECP"/PG                                                                        8.75/8.75                                                                          8.1    9.5  8.1  17.3                                       __________________________________________________________________________     .sup.1 Weight percent based on the weight of the continuous (fluid) phase     .sup.2 High temperature, high pressure fluid loss at 20° F. and 50     psi pressure differential.                                               

As can be seen, the composition comprising soluble and insolublealcohols (PECP/PG) gave better results than would have been predictedfrom the additive effects of each alone.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

What is claimed is:
 1. A method for drilling and cementing,comprising:drilling a wellbore with a drill string comprising a drillpipe utilizing a drilling fluid comprising water, blast furnace slag, asilicate and a retarder; circulating said drilling fluid down said drillpipe and up an annulus between said drill pipe and walls of saidborehole, thus laying down a filter cake on said walls of said boreholeduring said drilling and producing a used drilling fluid and producing aused drilling fluid; withdrawing said drill string and inserting a pipe,thus creating an annulus between said pipe and said walls of saidborehole; incorporating an activator system into a portion of said useddrilling fluid to produce a cementitious slurry; and displacing saidcementitious slurry into at least a portion of said annulus between saidpipe and said walls of said borehole.
 2. A method according to claim 1wherein said activator system comprises at least one of lithiumhydroxide, lithium carbonate, sodium silicate, sodium fluoride, sodiumsilicofluoride, magnesium hydroxide, magnesium oxide, magnesiumsilicofluoride, zinc carbonate, zinc silicofluoride, zinc oxide, sodiumcarbonate, sodium bicarbonate, titanium carbonate, potassium carbonate,potassium bicarbonate, sodium hydroxide, potassium hydroxide, potassiumsulfate, potassium nitrate, sodium or potassium aluminate, potassiumnitrite, calcium hydroxide, sodium sulfate, copper sulfate, calciumoxide, calcium sulfate, calcium nitrate and calcium nitrite.
 3. A methodaccording to claim 1 wherein said cementitious slurry is produced byalso incorporating a solid component selected from pozzolan or Portlandcement into said used drilling fluid.
 4. A method according claim 3wherein said solid component is Portland cement.
 5. A method accordingto claim 3 wherein said solid component is fly ash.
 6. A methodaccording to claim 3 wherein said solid component is incorporated in anamount within the range of 1 to 100 percent by weight based on theweight of blast furnace slag in said used drilling fluid.
 7. A methodaccording to claim 1 wherein said activator system comprises additionalblast furnace slag and a mixture of sodium hydroxide and sodiumcarbonate and said retarder is an organic acid.
 8. A method according toclaim 1 wherein said retarder is an organic acid, said activator systemcomprises a mixture of 2 to 6 lbs/bbl of sodium hydroxide in conjunctionwith 7 to 21 lbs/bbl of sodium carbonate and wherein additional blastfurnace slag is added in addition to said sodium hydroxide and sodiumcarbonate so as to give a total blast furnace slag concentration in saidcementitious slurry within the range of 100 to 300 lbs/bbl.
 9. A methodaccording to claim 8 wherein said water is seawater, said blast furnaceslag has a particle size within the range of 4,000 to 9,000 cm² /g anddrilling fluid comprises in addition a fluid loss control additiveselected from starch and clay.
 10. A method according to claim 9 whereinsaid fluid loss control additive comprises said clay.
 11. A methodaccording to claim 9 wherein said fluid loss control additive comprisesboth said clay and said starch and wherein said clay is prehydratedbentonite.
 12. A method according to claim 1 wherein said retarder is anorganic acid.
 13. A method according to claim 1 wherein, after saidcirculating of said drilling fluid, said drilling fluid is displaced anda fluid containing an activator system circulated through said annulusbetween said drill pipe and said borehole wall to set said filtercake;thereafter said fluid containing said activator system is displacedwith drilling fluid; and additional drilling is carried out prior tosaid withdrawing of said drill pipe.
 14. A method according to claim 1wherein said drilling fluid contains lime and partially hydrolyzedpolyacrylamide.
 15. A method according to claim 1 wherein said drillingfluid contains no partially hydrolyzed polyacrylamide.
 16. A methodaccording to claim 1 wherein said drilling fluid comprises in addition,a secondary viscosifier selected from the group consisting ofbiopolymers and starch.
 17. A method according to claim 16 wherein saidviscosifier comprises starch.
 18. A method according to claim 17 whereinsaid viscosifier comprises a biopolymer, said drilling fluid comprises,in addition, lime, and wherein said biopolymer is added after said lime.19. A method according to claim 1 wherein said silicate is sodiumsilicate.
 20. A method according to claim 1 wherein said drilling fluidcomprises, in addition, a fluid loss additive, a secondary weightmaterial, a secondary shale stabilizer, and a biopolymer secondaryviscosifier.
 21. A method according to claim 20 wherein said fluid lossadditive is selected from the group consisting of synthetic polymers,starch and bentonite clay, said secondary weight material is barite andsaid secondary shale stabilizer lime.
 22. A method according to claim 1wherein said silicate is sodium silicate.
 23. A method for drilling andcementing, comprising:drilling a wellbore utilizing a drilling fluidcomprising water, sodium chloride, 10 to 80 lbs/bbl of blast furnaceslag having a particle size such that it exhibits a surface area withinthe range of 4,000 cm² /g to 9,000 cm² /g, a synthetic polymer fluidloss control agent, starch, a welan gum biopolymer viscosifier, a watersoluble carbohydrate polymer deflocculant, a sodium silicate viscosifierand shale stabilizer, bentonite, and barite; thereafter incorporatinginto said drilling fluid an activator system comprising a mixture of 2to 6 lbs/bbl of sodium hydroxide in conjunction with 7 to 21 lbs/bbl ofsodium carbonate and additional blast furnace slag in an amountsufficient to give a total blast furnace slag concentration in saidcementitious slurry within the range of 100 to 300 lbs/bbl, to produce acementitious slurry; and displacing said cementitious slurry into saidwellbore to effect cementing and wherein said drilling fluid contains nopartially hydrolyzed polyacrylamide or carboxymethyl cellulose.
 24. Amethod according to claim 23 wherein said cementing is primarycementing.
 25. A method of drilling and cementing, comprising:drilling awellbore with a drill string comprising a drill pipe utilizing adrilling fluid comprising water, blast furnace slag, a silicate and aretarder; circulating said drilling fluid down said drill pipe and up anannulus between said drill pipe and walls of said wellbore thus layingdown a filter cake on said walls of said wellbore during said drillingthus producing a used drilling fluid, said wellbore being disposed in aformation having sufficient heat that heat is removed by saidcirculating of said drilling fluid; withdrawing said drill string andinserting a pipe, thus creating an annulus between said pipe and saidwalls of said borehole; adding additional blast furnace slag to saidused drilling fluid to produce a cementitious slurry; and displacingsaid cementitious slurry into at least a portion of said annulus; andmaintaining said cementitious slurry in said at least a portion of saidannulus until said heat from said formation activates said cementitiousslurry to thus cause said cementitious slurry to set into a cement.